Measured current

Thermal Transducers Infrared radiation generally does not have sufficient energy to produce a measurable current when using a photon transducer. A thermal transducer, therefore, is used for infrared spectroscopy. The absorption of infrared photons by a thermal transducer increases its temperature, changing one or more of its characteristic properties. The pneumatic transducer, for example. 

Each of these experimental designs also uses a different type of instrument. To aid in understanding how they control and measure current and potential, these instruments are described as if they were operated manually. To do so the analyst... 

In coulometry, current and time are measured, and equation 11.24 or equation 11.25 is used to calculate Q. Equation 11.23 is then used to determine the moles of analyte. To obtain an accurate value for N, therefore, all the current must result in the analyte s oxidation or reduction. In other words, coulometry requires 100% current efficiency (or an accurately measured current efficiency established using a standard), a factor that must be considered in designing a coulometric method of analysis. 

Precision Precision is determined by the uncertainties of measuring current, time, and the end point in controlled-current coulometry and of measuring charge in controlled-potential coulometry. Precisions of +0.1-0.3% are routinely obtained for coulometric titrations, and precisions of +0.5% are typical for controlled-potential coulometry. 

An electrochemical method in which we measure current as a function of the applied potential. 

Nonfaradaic Currents Faradaic currents result from a redox reaction at the electrode surface. Other currents may also exist in an electrochemical cell that are unrelated to any redox reaction. These currents are called nonfaradaic currents and must be accounted for if the faradaic component of the measured current is to be determined. 

Correcting for Residual Current In any quantitative analysis the signal due to the analyte must be corrected for signals arising from other sources. The total measured current in any voltammetric experiment, itot> consists of two parts that due to the analyte s oxidation or reduction, and a background, or residual, current, ir. 

Two methods are commonly used to correct for the residual current. One method is to extrapolate the total measured current when the analyte s faradaic current is zero. This is the method shown in the voltammograms included in this chapter. The advantage of this method is that it does not require any additional data. On the other hand, extrapolation assumes that changes in the residual current with potential are predictable, which often is not the case. A second, and more rigorous, approach is to obtain a voltammogram for an appropriate blank. The blank s residual current is then subtracted from the total current obtained with the sample. 

A nearly universal GC detector in which the solutes are combusted in an H2/air flame, producing a measurable current. 

Fisher s least significant difference a modified form of the f-test for comparing several sets of data. (p. 696) flame ionization detector a nearly universal GC detector in which the solutes are combusted in an H2/air flame, producing a measurable current, (p. 570)... 

The sohd line in Figure 3 represents the potential vs the measured (or the appHed) current density. Measured or appHed current is the current actually measured in an external circuit ie, the amount of external current that must be appHed to the electrode in order to move the potential to each desired point. The corrosion potential and corrosion current density can also be deterrnined from the potential vs measured current behavior, which is referred to as polarization curve rather than an Evans diagram, by extrapolation of either or both the anodic or cathodic portion of the curve. This latter procedure does not require specific knowledge of the equiHbrium potentials, exchange current densities, and Tafel slope values of the specific reactions involved. Thus Evans diagrams, constmcted from information contained in the Hterature, and polarization curves, generated by experimentation, can be used to predict and analyze uniform and other forms of corrosion. Further treatment of these subjects can be found elsewhere (1—3,6,18). 

FIG. 24-14 Dissolved-oxygen electrodes a) polarographic (impress breakdown voltage for oxygen measure current) (h) voltametric (measure electromotive force). 

Specificalions for current transformers General requirements Measuring current transformers 2705 Pan 1/1992 Pan 2/1992 BS 7626/1993... 

In all electrical measurements, current and voltage measuring instruments with two terminals are employed. The object being measured similarly has two termi-... 

Fig. 6-10 (right) Specimen holder for measuring current yield. 

Magnesium anodes are usually built into the object to be protected through isolating sockets or holes (see Fig. 20-6) and joined to them with cables. They must be readily accessible and easily exchangeable for convenient control [4]. The directions for use have to indicate the necessity for an inspection after 2 years of operation. During operation, control can be exercised by electrical measurements (current, resistance). In addition, acoustic and optical methods exist to determine the amount of anode consumption [4]. The life of the anodes is usually more than 5 years (see Section 6.6). 

Step 7 Measuring Current Levels of Waste Reuse and Recycling... 

Although the effects of dielectric constant change and strain have a strong effect on the current during wave transit time, the current at a time about j transit time is close to the value for the linear relation. Thus, based on Eq. 5.7, the wavespeed can be computed from the measured current and the measured polarization data. The approximate agreement between currents calculated from the polarization data and the wavespeed data confirms that the wavespeed values currently available are reasonable. 

Fig. 5.12. Stress versus time responses (measured currents) for (a) fee 28.5-at. % Ni above 2.5 GPa (25 kbar), (b) below 2.5 GPa, and (c) for bcc 28.5-at. % Ni, reveal substantial differences in mechanical response. Such records at different input stresses are used to determine the various stress-volume relationships (after Graham et al. [67G01]). Time increases from right to left. Timing waves (upper sinusoidal signal) are 10 MHz.

---